1. Field of the Invention
The present invention relates generally to an improvement in a diaphragm apparatus for use as a pressure-responsive switch or the like, and more particularly to a diaphragm apparatus having a magnetically induced hysteresis characteristic to reduce chattering.
2. Description of the Prior Art
A typical conventional diaphragm apparatus for use as a pressure-responsive switch or the like has a structure and operation as described hereafter with reference to FIG. 1, which is a sectional side view of the conventional diaphragm apparatus. The diaphragm apparatus has a diaphragm 4 in a case 1. When pressure in a vacuum tank T rises above a predetermined level, that is, when a pressure difference between a first partitioned space A connected to the vacuum tank T and a second partitioned space B exposed to open space air is smaller than a predetermined amount, the diaphragm 4 is biased to the right in FIG. 1 by a compressed coil spring 6. The spring 6 is held between a receiving washer 7 on an inside wall and a spring receiving seat 51 fixed to the center of the diaphragm 4. A moving contact 5 is thereby caused to contact another contact 3 fixed to the center of a plastic cap 2 of the case 1. As a result, an electric circuit of a motor M of a vacuum pump P is closed thereby operating the vacuum pump. Thereafter, the pressure of the vacuum tank reaches a predetermined low pressure, and the pressure difference between the first partitioned space A and a second partitioned space B becomes larger than a predetermined amount. The diaphragm 4 is then biased to the left in FIG. 1 as a result of the pressure difference now overcoming the force of the compression spring 6. The moving contact 5 separates from the fixed contact 3, deenergizing the motor M of the vacuum pump P.
In such a conventional diaphragm apparatus, since the diaphragm 4 is driven by the pressure difference between the first partitioned space A and the second partitioned space B, a first pressure difference to make the moving contact 5 contact the fixed contact 3 and a second pressure difference to make the moving contact 5 separate from the fixed contact 3 are substantially the same. Thus, the closing and opening of the motor circuit occur too frequently, responding, in practice, to every slight change of pressure in the vacuum tank T. This induces chattering of the diaphragm and moving contact 5, thereby shortening the lives of the moving contact 5, fixed contact 3 and motor M, and inducing operating problems within the related system.